Glutamic acid has been known as a main excitatory neurotransmitter that regulates high-order functions such as memory and learning in the central nervous system of mammals. Glutamate receptors are broadly classified into two types of receptors, namely, ionotropic glutamate (iGlu) receptors, and metabotropic glutamate (mGlu) receptors that are G-protein coupled receptors (GPCR). The iGlu receptors are classified into three types of receptors based on their agonist specificity; namely, N-methyl-D-aspartate (NMDA) receptors, α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors, and kainic acid receptors. On the other hand, the mGlu receptors include 8 subtypes (mGlu 1-8), and they are classified into group I (mGlu1 and mGlu5), group II (mGlu2 and mGlu3), and group III (mGlu4, mGlu6, mGlu7, and mGlu8), based on conjugate communication system and pharmacological properties. The group II and group III mGlu receptors are mainly expressed in the nerve ending in the form of an autoreceptor or a hetero receptor. These mGlu receptors suppress adenylate cyclase via a Gi protein and regulate specific K+ or Ca2+ channel activity.
In recent years, it has been reported that a glutamic acid concentration is changed in the cerebrospinal fluid and plasma of psychiatric patients suffering from mood disorder, anxiety disorder, schizophrenia and the like. It has been suggested that abnormity in the nerve functions of glutamic acid be associated with psychiatric diseases. An antagonist of group II mGlu receptor, among glutamate receptors, exhibits an antidepressive action and/or an anxiolytic action in various animal models (Non Patent Literature 1). Thus, it has been suggested that the group II mGlu receptor antagonist be likely to act as a novel antidepressive and/or anxiolytic agent. Moreover, it has also been suggested that the group II mGlu receptor antagonist exhibit the effect of a cognitive function enhancing agent (for dementia and Alzheimer's disease) (Non Patent Literature 2).
Recently, Patent Literatures 1 to 3 have reported a compound having an antagonistic effect on the group II mGlu receptor and having an ethynyl structure. However, these patent literatures neither disclose nor suggest a compound having an ethynyl-pyrazole skeleton.